Group-address system



Dec. 8, 1936.

E. L. BOWLES GROUP ADDRESS SYSTEM Filed Sept. 28, 1932 '3 Sheets-Sheet 1 r W mw w 1 r 1% .wfi t wfd IL m Q 2. 4 24 E. L. BOWLES GROUP ADDRESS SYSTEM Dec. 8, 1936.

Filed se t. 28, 1932 :s Sheet s-Sheet s AMPLIFIER s Z MW m f M w w @tfo W165 I Patented Dec. 8, 1936 UNITED STATES PATENT OFFICE 2,063,224 GROUP-ADDRESS SYSTEM Edward Lindley Bo'wles, Wellesley Farms, Mass. Application September 28, 1932, Serial No. 635,211

- 7 Claims.

The present invention relates to group-address systems, and more particularly those in which: first, the voice of a speaker making an address, music, or other form of sound energy that it is desired to transmit; in amplified form, to an phone is usually placed immediately before the speaker, and the loud-speaker horn some distance away; in fact, as faraway as isconveniently possible. I

To place the microphone near the loud speak er has involved difficulties, for if any appreciable amount of sound energy coming from the loud speaker should reach the microphone, howling effects would be produced, of so objectionable a nature as to render the system practically inoperative. Not only has it been necessary. to separate the loud speaker and the microphone,

therefore, but it has been considered advisable properly to orient the loud speaker, even when at a distance.

The separating of the microphone and the loud speaker has the advantage that it lends itself well to the covering of large areas, where relatively large energy outputs are desired. A very objectionable artificiality is thus, however, created. The audience observes the speaker on platform or pulpit, and sees his lips move, but must accustom itself to the sound coming from an entirely different point.- There is a consequent constant eflort of the audience to reconcile such dissociated sound and vision manifestations, as if ones eyes were set in one place and ones ears in another.

An object of the invention, accordingly, is to provide a novel, group or public-address system that shall overcome this difliculty.

A further object is to provide a novel, groupaddress system with the use of which a speaker fled sound shall appear to come directly from the speaker's lips, thus eliminating the above-de-, scribed artiflciality.

Another object is to provide. a novel, groupaddress system with the use of which a speaker may address his audience without discomfort either to himself or the audience; for, according to the present invention, neither the speaker nor the audience need be aware of the fact that the speakers voice, before it reaches the audience, has become supplanted by an amplified facsimile-of the same.

As the horns,- especially the cluster horns, ordinarily employedin group-address systems, detract from the beauty of the surroundings, particularly in such places as churches, still 'ani other object of the invention is to conceal the sound pickup and amplifying. or other equipment, so that the audience shall not'be conscious 10 of the recreation of the original sound, such as that produced by the speaker's voice.

The invention will now be explained in connection with the accompanying drawings; in with Fig. 1 is a perspective view of a lecturestand or lectern arrangement embodying the present invention; Fig. 2 is a back elevation of the same, with the back cover removed; Fig. 3 is a side elevation of the same, with the near side removed; Fig. 4 is a vertical section taken upon the line 4-4 of Fig. 2, looking in the direction of the arrows; Fig.5 is an elevation, partly in section, of a modification; Fig. 6 is a perspective of a further modification, involving a complete, group-addressunit on a stage of a theatre or lecture hall; Fig. 7 is a diagrammatic view of circuits and apparatus arranged and constructed in accordance with this invention; and Fig. 8 is a view of a further modification.

The lecture-stand or lectern I may be fixed, or it may be portable, so that it may be rolled or otherwise moved from one class room or lecture hall to another of a school or other building. It is provided with a base 2, upon which rests a frame [6, having side walls or panels 4, a front cover wall or panel II, shown removed in Fig. 2, and a top wall 6. An innershelf M, below the top wall 6, separates an intermediately disposed housing l0, above the shelf M. from a lower housing, for a container or box 5, below the shelf ll. The side walls or panels 4, like the panel ll, may be removable. If the walls or panels of the lectern aremade of relatively heavy wood, they will not act as diaphragms, and will not vibrate as a whole, at an objectionable, low frequency. A housing l3 rests on the top wall Band is provided with a desk cover board I5 on which may rest a thin, sponge-rubber mat 25, for reducingthe noise that may be caused by direct contact of a speaker's papers, watch, and other articles with the wood top of .the desk cover board I5.

- A transmitter unit 9, comprising a condenser microphone 3 and its associated amplifier, is judiciously arranged in the housing 13, just below audience. similarly covered, so that not even the speaker the top thereof. An amplifying'unit 1 is disposed in the intermediately disposed housing ID, on the shelf M. A loud speaker unit 2| is internally housed in the container 5. The loud speaker being thus selfcontained and acoustically insulated from the surrounding lectern structure, it is possible materially to reduce any sound transmission from the loud speaker system to the,lec-

tern body. The loud speaker is provided with a cone 23, neatly covered with a sound-porous cloth or metal netting 8 that, by proper selection, can be made to blend artistically in with the rest of the apparatus to form a neat front panel, rendering' the loud speaker 2| inconspicuous to the The microphone opening 12 may be shall be aware of its presence.

' Thecondenser transmitter or microphone unit 9 is disposed in acoustic-insulating and resonantsuppressing material ll that acoustically insu- ,lates the microphone 3 from the material of which is made the desk housing l3, comprising the desk cover board [5 and the top wall 6. The material I! may befelt, packed about the condenser-transmitter unit 9 in two ways: first, beneath the unit, to act as a cushion, substantially to eliminate acoustic conduction from thebody structure of the lecternto the transmitter unit 9;, and secondly, to fill spaces within the lectern structure, which would otherwise tend to resonate atsome sound frequency. The microphone unit 9 is thus acoustically cushioned, and also the-objectionabletendency to cavity resonance is overholes for the purpose of making the sound absorption more complete. The celotex may, in turn, be covered with felt.

The inside walls of the lectern I may likewise be all covered or lined with some material, like felt, to a degree suflicient to eliminate all residual tendency for. the lectern walls or panels to resonate as diaphrag'ms. The kinds and quantity of lining material will depend upon the kind of wood used, the thickness, the inside dimensions and the' type of the deadening material used.

Other sound-absorbing materials may also be used; in combination, not only to prevent the transmission of sound from within the box 5 to the lectern frame l6, but also to absorb the sound radiated from the back of the cone speaker, thus giving it a frequency-response characteristic such as. it would have if it were in a baflle, operating into free spacemn both sides. The presence of the acoustically-absorbing material in the box 5 thus :renders it possible to prevent any cavity resonance. therein. Such cavity resonance, of course,'would have a serious effect on the desired frequency response characteristics of the loud 1 speaker.

It thus becomes possible to mount the various parts of the group-address system in a single 'lectern I, very close to the speaker, and where they are completely hidden from view. The

speakers voice is satisfactorily recreated and amplified with relative freedom for acoustic feedback either through the material of which the is desirable to fix the lectern permanently in -position, as in the case of a church pulpit, and

if there is sufficient space below the floor, the

horn may be relatively long and straight, and extend below the base of the lectern and below the floor, as illustrated in Fig. 5. I

It is' sometimes convenient to use two micro--v phones 3, instead of only one, as illustrated in Fig. 8. The two microphones may be placed side by side, near the center of the lectern desk housing l3, as in Fig. 2, orone may be placed at each extremity of the desk l3, as shown in Fig. 8.

It is often convenient to have the volume of the sound output from the lectern, group-address system controllable from some remote point. As illustrated in Fig. 6, for example, an individual in the audience may monitor the output of the group-address system from a point 9| at which he is seated. This type of gain in volume control insures a proper coverage of the audience and, at the same time, makes it possible to adjust to that point of amplitude which it simulates the normal amplitude of the speakers voice; Without such direct control, group-address systems are often adjusted to put out so very much energy that the level-is obviously artificial.

The electrical connections may be as diagrammatically illustrated in Fig. 7. The condensertransmitter unit 9 is illustrated as comprising a condenser transmitter 3, associated with an amplifier 65 and an output transformer 61, all in a shielded case. Other microphone arrangements may alsobe employed; as is obvious. The microphone unit 9 is connected by means of shielded leads II, connected to terminals 69 that may be plugged into sockets I3, the shield being grounded at 89, to a remote, volume-control unit, shown as a conventional T-type", attenuator ll, though any other convenient type of control may be used. This unit is housed in a shielded box 15 and is controlled by a calibrated dial 19. The volume-control unit is connected with an equalizer 35; that may be of any desired type. The equalizer 35 is arranged so that it is possible to adjust the relativeproportion of lowfrequency and high-frequency energy affecting the'power amplifier 'I. By means of this equalizer unit, it is possible to compensate for the over-all, frequency-response characteristic, of the lectern, group-address unit, when operating in a given environment.

The unit 35 comprises three vacuum-tube amplifiers 45, 41 and 49, associated with an input transformer 5| and an output transformer 53.

The tube 45 is coupled to the, tube 41 by means of a variable inductor 31 and a variable resistor 39,

,in series, a by-pass condenser 55 and a conventional, gridleak potentiometer 51' being also shown. The tube 41 is coupled to the tube 49 by 75 aocaaaa resistor 4|, 2. shunt-feed choke 59 furnishing the B-battery supply to the plate of the tube 41; a

by-pass condenser 5| and a conventional, gridenergy. Thedegree of suppression or emphasis is controlled by dials 8|, 83. The adjustment of p the value of the condenser 43 and the resistor 4| will control the relative amplification of the high, audio-frequency energy. The degree of suppression or emphasis is controlled by 'dials 85 and 81. With sufliciently high values for the resistors 39 and 4|, the unit 35 will have a uniform amplifying efiect over the entire band of desired acoustic frequencies.

The resistors 39 and 4|, the inductor 31 and the condenser 43 may, of course, be replaced by other shunt elements. In the plate circuit of the tube 41, for example, the condenser 43 may be replaced by a condenser in series with an inductor, variably tunable to series resonance; or, again, such a series-resonance unit may be imcluded in an additional stage of amplification. According to the illustrated embodiment of the invention, however,-any adjustments of relative intensity of the different portions'of the frequency spectrum may be made on the inductor 31, and the resistor 39, and/or the condenser 43 and the resistor 4| in a mutually exclusive manher. The adjustment of one of these plate-circuit, frequency-control elements does not affect the operation or the adjustment of any other.

This, of course, would not be the case if both.

these elements were connected in the same circuit, and not electrically divorced by means of an interposed, unilateral, vacuum-tube amplifier,

'suchas the amplifier 41.

The monitoring individual may thus have be- .fore him the volume-control element 11 and also,

if necessary, the equalizer element 35. By locally adjusting the equalizer 35, he may increase the degree of intelligibility of speakers with certain types of voices.

' Further modifications will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

tioned in the housing between the loud-speaker vand the microphone for preventing the said appreciable actuation of the microphone.

2. A group-address system having, in combination, a housing, a loud-speaker in the housing 'oriented to project sound out of the housing, a

microphone in the housing at a position such that its sensitive surface is disposed in the acoustical shadow of ,the loud-speaker but close enough to the loud-speaker so that sound from the loud-speaker would be adapted to travel into the shadow to the microphone in appreciable quantity and thus appreciably actuate the microphone,,and acoustic-insulating means positioned in the housing between the loud-speaker and the microphone for preventingthe said appreciable actuation of the microphone.

3. a group-address system having, in combination, a housing, a loud-speaker in the housing oriented to project sound out of the housing, a microphone in the housing at a position such that its sensitive surface is'disposedin the acoustical shadow of the loudspeaker but close enough to the loud-speaker so that sound from the loudspeaker would be adapted to travel into the shadow to the microphone in appreciable quantity and thus appreciably actuate the microphone, an amplifier in'the housing, and acousticinsulating means positioned in the housing between the loud-speaker and the microphone for preventing the said appreciable actuation of the microphone. I

4. A, group-address system having, in combina-- tion, a lectern comprising a housing having'a base and a'frame supported by the base having side walls and a top wall, a container in the housing, a loud-speaker in the container oriented to project sound out of the housing, a. microphone positioned so that its sensitive surface is disposed in the acoustical shadow ofthe loud-speaker but close enoughto the loud-speaker so that sound from the loud-speaker would be adapted to travel into the shadow to the microphone in appreciable quantity and thus appreciably actuate the microphone, and acoustic-insulating means positioned in the housing between the container and the -microphone for preventing the said appreciable a shelf below the top wall, whereby a first housing is formed abovethe shelf and a second housing is formed below the shelf, a container in the second housing, a loud-speaker in the container oriented to project sound out of the housing, an amplifier disposed in the first housing, a microphone positioned so that its sensitive surface is disposed in the acoustical shadow of the loudspeaker but close enough to the loud-speaker so v that sound from the loud-speaker would be adapted to travel into the shadow to the microphone in appreciable quantity and thus appreciably actuate the. microphone and the amplifier, and

acoustic insulating means positioned in the housings between the container, the amplifier and the microphone for preventing the said appreciable actuation of the microphone and the amplifier.

6.'A group-address system having, in combination, a lectern having a base, a frame supported by the base having side walls and a top wall, a closed housing disposed on the top wall, ashelf below the top wall, whereby an intermediately disposed housing is formed above the shelf and a lower housing is formed below the shelf, a container in the lower housing, a microphone disposed in the closed housing, a loud speaker in the container, an amplifier disposed in the intermediately disposed housing, acoustic-insulating and resonance-suppressingmeans in the closed housing in which the microphone is disposed,

acoustic insulating and resonance-suppressing material in the intermediately disposed housing in which the amplifier is disposed, acoustic-' insulating and resonance suppressing material 10 the lower housing, a microphone disposed in the closed housing, a loudspeaker in the container, acoustic-insulating and resonance-suppressing means in the closed housing in which the microphone is disposed, acoustic-insulating and resonance-suppressing material in the lower housing in which the container is disposed, and acousticinsulating and resonance-suppressing material in the container in which the loudspeaker is disposed.

EDWARD L. BQWLES. 

